Our goal is to develop a reliable conduit (synthetic or biograft) for aortocoronary bypass for patients lacking suitable autologous grafts. Factors influencing the thrombogenicity and patency of 4 mm ID grafts will be studied in the canine carotid and coronary artieries. In vivo effects on graft perfomance of graft character, blood flow rate and pattern, blood composition and coagulability (altered and not altered) will be measured. Performance assessment involves measurement of coagulum of area and thickness, as well as patency. These data will be subjected to statistical analysis.